Effect Of Plastic Film Residue On Transportation Of Water And Nitrate And Seedling Root Of Crops

With the wide use of mulching film, a growing number of plastic residual film left in soil, which causes the severe problem of “White Pollution” in China and has a heavy adverse effect on farming and ecological environment. Water and nitrogen are the main factors affecting the crops growth. Owning to much plastic residual film in the soil, the residual film may change soil physical structure and hinder the movement of water and nitrate in the soil. Root is active in absorbing and composing matters for crops.Residual film has direct contact with root in the soil, which may make an impact on root growth. Our research is to study the effect of plastic residual film on soil infiltration, water and nitrogen distribution and seedling root though simulated test which sets up 7 residual film levels.(1) Residual film can hinder the movement of wetting front. Within the range of 0~360kg/hm~2,90kg/hm~2 treatment shows minimum horizontal distance in 50 minutes. And in 175 minutes, treatments with increment of residual film give rise to decreases in horizontal distance. The mass density of residual film has no obvious effect on the vertical distance while there is a significant difference between residual film treatments and CK. The process of wetting distance along with irrigation duration follows the law of power function. With the increment of residual film the volume of wetting body decreases while irregular degree of wetting body increases. The infiltration could be well described by the Kostiakov Formula, which correlation coefficients were over 0.984. Residual film may increase the steady infiltration rate and make wetting body small resulting in that water stays in the wetting body.When the mass density of residual film is more than 360 kg/hm~2, excessive amounts of residual film would add soil macropore heavily, which increase wetting distance and wetting body and decrease steady infiltration rate.(2) Surface wetted radius has a positive relationship with mass density of residual film. Within the range of 0 ~ 360kg/hm~2, water may stay in upper part of wetting body due to residual film, and distribution of water in the wetting body is uneven. The more the residual film is, the greater the unevenness. When the mass density of residual film is over 360 kg/hm~2, water content will increase in lower area of the wetting body owning to the preferential flow caused by excessive amounts of residual film. Water migration patterns are aggravated by the random distribution of residue in the soil, resulting in that variations of the water content in the soil along vertical and horizontal depth present erratic change.(3) Within the range of 0~360kg/hm~2, nitrate may stay in upper part of wetting body due to residual film, and distribution of nitrate in the wetting body is uneven. The more the residual film is, the greater the unevenness. When the mass density of residual film is over 360 kg/hm~2, nitrate content will increase at the boundary of the wetting body owning to the preferential flow caused by excessive amounts of residual film. Nitrate migration patterns are aggravated by the random distribution of residue in the soil, resulting in that variations of the nitrate concentration in the soil along vertical and horizontal depth present erratic change(4) Root growth and physiological index for cotton and maize increase firstly and then decrease with the increment of residual film. Whether the root length, average root diameter and root surface area or the root activity, CAT activity and POD activity, the peak values appear on the mass density of 90 or180 kg/hm~2. It is concluded that appropriate residual film between 90 and 180 kg/hm~2 may promote the growth of seedling root, and residual film which is over that range will hamper the growth of seedling root.